FIG. 5 is a front view of an injection molding apparatus provided with a convention resin-flow observing apparatus. The injection molding apparatus 100 includes a base 101, on which are placed an injection unit 106 and a mold clamping unit. The injection unit 106 includes a nozzle 102, heating cylinder 103, screw drive section 104 and hopper 105, etc., and the mold clamping unit includes a mold 108 and is covered with a safety cover 107. Fluid pressure unit and input/output unit 109 are provided within the base 101. Further, the mold 108 has fitted therein a lens 111 to provide an observation window, through which a user or human operator is allowed to observe molten resin flowing in the mold 108. The lens 111 is a circular lens made of transparent glass or plastic material.
In precision molding techniques today, it is extremely important to know exactly the flowing behavior of the molten resin. Valuable data may be acquired if a flow of molten resin can be observed through the lens 111.
However, for pressure resisting reasons, it is difficult to increase the diameter of the lens 111, and the lens 111 must be limited to a relatively small diameter. With the lens 111 having a small diameter, only a narrow resin-flow observation range can be provided, which thus permits acquisition of only a limited quantity of data. Therefore, there has been a demand for a more sophisticated technique that can considerably increase the resin-flow observation range. In addition, fitting the lens in the mold would increase the necessary number of manufacturing steps and necessary cost of the resin-flow observing apparatus, and therefore there has also been a demand for a less expensive resin-flow observing apparatus or experiment apparatus.